1. Field of the Invention
The present invention relates to a water filling technique capable of filling a reactor water level gauge with water even in an unexpected abnormal event where a reactor building is brought into a highly radioactive environment.
2. Description of the Related Art
In a nuclear power plant, a reactor holds water, and hydraulic head pressure of water is measured to measure a reactor water level. An instrumentation pipe of a reactor water level gauge that measures a reactor water level is filled with water.
As shown in FIG. 11, such instrumentation pipe 1a of a reactor water level gauge 1 is connected via a gauge test valve 2 to a pump 3. The gauge test valve 2 is opened, and the pump 3 is used to fill the instrumentation pipe 1a of the reactor water level gauge 1 with water from a makeup water system (MUW) or water in a tank 4 left overnight in terms of preventing inflow of air.
In a reactor building 5, the makeup water system (MUW) is provided close to the instrumentation pipe 1a of the reactor water level gauge 1, and an MUW main valve 7a of the MUW pipe 7 and the gauge test valve 2 are connectable by a flexible pipe. The gauge test valve 2 is opened, and the MUW main valve 7a is opened to fill the instrumentation pipe 1a of the reactor water level gauge 1 with water, and a reactor water level can be measured by the reactor water level gauge 1.
However, due to an earthquake, in the reactor water level gauge 1, water in the instrumentation pipe 1a in a reactor containment vessel 6 evaporates to cause a malfunction or an instruction error of measuring gauges. In addition, after the earthquake, the reactor containment vessel 6 is brought into an environment of 100° C. or more, the water in the instrumentation pipe 1a continuously evaporates without being condensed to cause an instruction error for measurement of the reactor water level. In FIG. 11, reference numeral 8 denotes a reactor pressure vessel, and reference numeral 9 denotes an existing transmitter.
Further, the reactor building 5 housing gauges is brought into a highly radioactive environment after the earthquake, the gauge test valve 2 through which the instrumentation pipe 1a of the reactor water level gauge 1 is filled with water is not accessible, making it difficult to fill the instrumentation pipe 1a with water.
For a conventional nuclear power plant, occurrence of an unexpected abnormal event such as an earthquake is not considered, and further, it is not assumed that the reactor building 5 is brought into a highly radioactive environment. Thus, inaccessibility to the gauge test valve 2 provided in the reactor building 5 is not considered.